I regret that after reaching out here on the Forum, and setting out a pretty honest account of your circumstances you have not had a second reply. I am glad you did meet Sophie_M, who gives good advice.
The reason it has taken so long is nothing to do with you personally, or the subject of your post, it is just that our system does not always work as we would like.
The final thing you said was you do not have a GP to go to and I'm wondering why as that is one important place to start. Feeling the way your do, anxious over your supervisor -who sounds a pain - plus the difficulties at uni, study and sleep. Add to that your uncomfortable reflections on the things you do.
All these seem to me to be much the same sort of things I've felt, and I have an ongoing anxiety condition plus bouts of depression. I too tried to 'make' myself better, but nothing worked until I got competent medical care.
Do you think it might be possible to see a GP despite what you said before? It might start with a uni councilor and go from there.
A lot of people do not want to worry their parents, however that's not always a good idea. I'm a parent, and the other parent I know are all the same as me. We really would want to know how our young person actually is, and then be able to take action to make things better. It's simply love. Do you think one of your parents might be easier to talk with?
Maybe you might also like to explain to your younger brother it is not him, it is you having difficulties - would he be old enough for you to do that? Many younger people think it is their fault when it is not (something I think you do yourself.)
Would you like to come back and talk some more? The answer would be a lot quicker next time:)